Simple PRNG implementation

prand.c

@@ -0,0 +1,47 @@
+#include "prand.h"
+#include <stdint.h>
+#include <stdio.h>
+#include <time.h>
+
+#define BUILD_SEED                                                             \
+    ((uint64_t)(__TIME__[0]) * (uint64_t)(__TIME__[1]) *                       \
+     (uint64_t)(__TIME__[3]) * (uint64_t)(__TIME__[4]) *                       \
+     (uint64_t)(__TIME__[6]) * (uint64_t)(__TIME__[7]))
+
+#define PRNG_SAVE_INTERVAL 50 // Save every 1000 calls to prand()
+
+static uint64_t seed = BUILD_SEED;
+
+uint64_t prand() {
+    seed = seed * 6364136223846793005ULL + 1;
+    return seed;
+}
+
+inline uint64_t prand_range(uint64_t min, uint64_t max) {
+    return min + (prand() % (max - min + 1));
+}
+
+void sprand(uint64_t s) {
+    if (s) {
+        seed = s;
+    } else {
+        rand_reseed();
+    }
+}
+
+void rand_reseed() { seed = BUILD_SEED; }
+
+#define PRAND_MAIN
+#ifdef PRAND_MAIN
+int main() {
+    // time(NULL) provides a somewhat unique seed at runtime
+    sprand(time(NULL));
+
+
+    uint64_t rn1 = prand();
+    uint64_t rn2 = prand();
+
+    printf("rn1 = %lu\n", rn1);
+    printf("rn2 = %lu\n", rn2);
+}
+#endif